Residue concentration measurement technology

ABSTRACT

A method and apparatus for measuring dissolved residue concentrations and particulate residue particle concentrations and size distribution in liquids, particularly colloidal suspensions. The method involves separating dissolved and particulate residues in liquids for subsequent analysis of the residue species. The method includes the steps of forming an aerosol from the liquid sample to be analyzed, evaporating the droplets in the aerosol to dryness, detecting and sizing the particles, and determining the liquid volumetric inspection rate. An apparatus for separating dissolved and particulate residues in liquids for determination of the concentrations of the two residue species as well as the size distribution of the particulate species is also disclosed. The apparatus includes a droplet former, a dryer communicatively connected to the droplet former, and a detector communicatively connected to the evaporator for detecting and sizing particles.

CROSS-REFERENCE TO RELATED APPLICATIONS, IF ANY

This application is a divisional of U.S. patent application Ser. No.13/068,396, filed May 10, 2011, issued as U.S. Pat. No. 8,573,034 on May10, 2011, which is a continuation in part of U.S. patent applicationSer. No. 12/357,088, filed Jan. 21, 2009, issued as U.S. Pat. No.8,272,253 on Sep. 25, 2012, which claims the benefit under 35 U.S.C.§119(e) of U.S. Provisional Patent Application Ser. No. 61/011,901,filed Jan. 22, 2008, which is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX, IF ANY

Not applicable.

BACKGROUND

1. Field

The present invention relates, generally, to analysis methods andapparatus for use with compositions of matter. More particularly, theinvention relates to a method and apparatus for measuring the size andconcentration of small particles and the concentration of dissolved,non-volatile residues in colloidal suspensions. Most particularly, theinvention relates to an apparatus and method for separating dissolvedand particulate residues in a colloidal suspension to determine both thesize distribution and concentration of the particulate species (i.e.insoluble particles) and the concentration of dissolved non-volatileresidue. The technology is useful, for example, for accurate measurementof particle size distributions and dissolved non-volatile content incolloidal suspensions. The invention is suitable for use in thesemiconductor device manufacturing industry, the ink manufacturingindustry, and in other fields.

2. Background Information

The invention provides methods and apparatus for measurement of ParticleSize Distributions (PSDs) and concentration of particulate Non-VolatileResidue (hereinafter “pNVR”) and the concentration of dissolvedNon-Volatile Residue (hereinafter “dNVR”) in colloidal suspensions.There are numerous applications in which the PSD and dNVR concentrationsin colloidal suspensions are important in determining the efficacy ofthe suspension. Examples include slurries used in chemical mechanicalplanarization (CMP) of silicon wafers, as well as wafers composed ofother materials, during semiconductor chip manufacturing andpigment-based inks. The PSD and dNVR content of CMP slurries determinesthe planarization rate, surface smoothness and scratch density on thewafer surface following the CMP process. All of these are important indetermining the finished semiconductor device yield and performance. Thesize distribution of pigment inks is important in determining colordevelopment while dNVR content is important in determining rheologicalproperties and stability of the inks.

Historically, technologies have been developed to measure “total”non-volatile residue (“dissolved” residue plus “particulate” residue) orto measure the particle size distribution in colloidal suspension.Techniques to separate and measure the two components of residuesimultaneously have not been developed insofar as is known prior to thepresent invention.

Total NVR (tNVR) has typically been measured using non-volatile residuemonitors (NVRM or NRM). These instruments work by forming an aerosol ofthe liquid, evaporating the liquid in the aerosol and measuring thenumber of particles in the aerosol. The instruments measure combineddNVR and pNVR and are typically used to measure the tNVR content inliquids that contain mostly dNVR (little pNVR present). They have beenused to measure filter retention of colloidal silica particles; however,measurement accuracy was compromised by interference caused by dNVR.

Measurement of particle size distributions in colloidal suspensions, hastypically been addressed using dynamic light scattering (DLS), laserdiffraction (fraunhofer diffraction) or centrifugal sedimentation. Thesemethods only measure relative PSDs. Insofar as is presently known, theycannot determine actual concentrations.

PSDs in colloidal suspensions have also been analyzed using acombination of electrospray and mass spectroscopy. Electrospray is usedto generate small droplets by subjecting the liquid to a high electricfield. The liquid must be moderately conductive and the droplets becomehighly charged during formation. High purity liquids typically have lowconductivity making the formation of small droplets difficult. Also, thehigh charge on the particles can result in particle agglomeration andmay cause other changes in particle properties. The agglomeration issuecan be addressed by exposing the aerosol to ionizing radiation.

For these and other reasons, a need exists for the present invention.

All US patents and patent applications, and all other publisheddocuments mentioned anywhere in this application are hereby incorporatedby reference in their entirety.

BRIEF SUMMARY

The present invention provides methods and apparatus for (a) separatingdNVR and pNVR in a colloidal suspension, (b) measuring the concentrationof dNVR in the suspension, (c) measuring the concentration of pNVRparticles larger than 5 nm in diameter or smaller in the suspension, and(d) measuring the size distributions of such pNVR particles. The methodand apparatus are practical, reliable, accurate and efficient, and arebelieved to fulfill a need and to constitute an improvement over thebackground technology.

In one aspect of the present invention, a method includes the steps of,providing a specimen of a colloidal suspension to be tested, isolatingsmall, uniformly sized droplets from the specimen, evaporating thedroplets to dryness, and counting and sizing the resulting particles.Two types of particles result from the isolation/evaporation process:(a) those from droplets that originally contained pNVR and (b) thosefrom droplets that contained only dNVR. The pNVR-free droplets formsmall particles consisting of dNVR when the volatile liquid is removed.If the droplets are sufficiently small and uniformly sized, each dropletwill contain either 0 or 1 particulate species and the particles formedfrom dNVR will be significantly smaller than the particulate (pNVR)species. By measuring the resulting PSD both the concentration of thedNVR (very small particles) and the PSD of the pNVR (larger particles)can be measured.

In another aspect of the present invention, an apparatus includes aNebulizer/Impactor and a Scanning Mobility Particle Sizers (SMPS). TheNebulizer/Impactor has means to form or form and isolate small,uniformly sized droplets from a colloidal suspension. The SMPSaccurately sizes and counts particles present after the small, uniformlysized droplets are dried to measure the PSD and concentration of thepNVR and the concentration of the dNVR.

A Nebulizer/Impactor combination is provided for generating an aerosolcomposed of multiple droplets of a colloidal suspension. TheNebulizer-Impactor includes a housing forming a mixing chamber having(i) a liquid entrance for receiving a sample liquid into the chamber,(ii) a primary orifice having a first diameter for receiving apressurized gas into the chamber for merger with the sample liquid togenerate an aerosol composed of multiple droplets of the sample liquidsuspended in the gas, and (iii) a secondary orifice having a secondarydiameter for conducting the aerosol out of the chamber. The secondorifice is less than a major dimension of the mixing chamber taken in adirection substantially perpendicular to an axis of the secondaryorifice, so as to restrict flow out of the mixing chamber to generate aback pressure in opposition to entry of the sample liquid and thepressurized gas into the chamber.

In contrast to other nebulizers in which the chamber exit is simply opento the downstream components with a diameter equal to that of thechamber, the exit orifice in the nebulizer has a diameter less than thatof the chamber, more preferably less than half the diameter chamber. Thediameter reduction provides a constriction that produces a higherkinetic energy mixing of the gas and liquid in the merger zone. As aresult, the nebulizer generates smaller droplets. The secondary orificealso helps direct the aerosol toward the impactor surface raising theimpactor efficiency.

Another factor reducing the droplet size produced by theatomizer/impactor is close axial positioning of an impactor justdownstream of the secondary orifice. The more closely spaced impactorremoves a greater proportion of the larger droplets.

In a preferred version of nebulizer/impactor, the impactor axial spacingfrom the secondary orifice is adjustable through movement of theimpactor. For example, a threaded mounting of the impactor to thenebulizer frame allows axial position adjustment by turning the impactorabout its longitudinal axis. The average size of the droplets in theaerosol leaving the nebulizer can be increased or decreased byrespectively enlarging or reducing the axial spacing between thesecondary orifice and the impactor. The average size can also bedecreased and the uniformity increased by making the shape of thehousing containing the secondary orifice conformal to the impactorshape.

The droplet size produced by atomizer/impactor also can be adjusted bychanging or selecting the secondary orifice. Reducing the diameter ofthe secondary orifice is believed to increase back pressure and reducedroplet size. It has been found useful to provide a secondary orificewith a diameter larger than that of the primary orifice. The ratio ofthe secondary orifice diameter to the primary orifice diameter can rangefrom slightly above one, to about two in versions that incorporate asecondary orifice.

The aspects, features, advantages, benefits and objects of the inventionwill become clear to those skilled in the art by reference to thefollowing description, claims and drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The present invention, and the manner and process of making and usingit, will be better understood by those skilled in the art by referenceto the following drawings.

FIG. 1 is a flow diagram of one embodiment of the method of the presentinvention.

FIG. 2A is a diagram illustrating an embodiment of the apparatus of thepresent invention.

FIG. 2B is a diagram illustrating an alternative embodiment of theapparatus of the invention.

FIG. 2C illustrates a system for measuring droplet size distributionsproduced by droplet formers.

FIGS. 3 A-C illustrate pneumatic, concentric and flow focusingembodiments of a nebulizer component of the apparatus of the invention.

FIG. 4 is a crossectional view of an embodiment of a plate impactorcomponent which is used in an embodiment of the apparatus of theinvention.

FIG. 5 is a crossectional view of an embodiment of a virtual impactorwhich is used in another embodiment of the apparatus of the invention.

FIG. 6 is a diagram showing impactor efficiency.

FIG. 7 illustrates an embodiment of a vibrating orifice generator usedin an embodiment of the apparatus of the invention.

FIG. 8 is a sectional side elevation view of an embodiment of the systemof the present invention including a combination nebulizer-impactor.

FIG. 9 is a sectional view of the combination nebulizer-impactor.

FIG. 10 is an enlarged view showing a portion of the nebulizer-impactorof FIGS. 8 and 9.

FIG. 11 is a graph of droplet size distributions produced by variouscombinations A, B, C and D of nebulizers with impactors.

FIG. 12 is a graph of differential concentration versus particle size,which shows the ability to size 30 nm particle PSL.

FIG. 13 is a graph of aerosol volumetric concentrations measured usingstandards containing 5.0×10¹⁷ nm3/mL of silica particles.

FIG. 14A shows pNVR particle size distributions in Colloidal DispersionA measured using Combination D apparatus of FIG. 12 with an SMPSdetector.

FIG. 14B shows pNVR particle size distributions in Colloidal DispersionA measured using dynamic light scattering.

FIG. 14C shows particles in Colloidal Dispersion A imaged using ScanningElectron Microscopy.

FIG. 15A shows the change in slurry number-weighted PSD over time duringhandling as measured using Combination D apparatus with an SMPS analyzervia a graph of differential number concentration versus particlediameter.

FIG. 15B shows the change in slurry volume-weighted PSD over time duringhandling as measured using Combination D apparatus with an SMPS analyzervia a graph of differential volume concentration versus particlediameter.

FIG. 15C shows the change in slurry PSD over time during handling asmeasured using Dynamic Light Scattering via a graph of differentialnumber concentration versus particle diameter.

FIG. 16A shows particle concentration measurement of a liquid containing0.1% by weigh pNVR silica particles and 1% by weight dNVR following a2000:1 dilution.

FIG. 16B shows particle concentration measurements of a liquidcontaining 0.1% by weigh pNVR silica particles and 1% by weight dNVRfollowing different dilution ratios.

FIG. 17 shows particle concentration measurements of a liquid containing2 populations of pNVR particles following different dilution ratios

FIG. 18A shows particle concentration measurements of a liquidcontaining pNVR silica particles and different concentrations of dNVR.

FIG. 18B shows the relationship between aerosol particle concentrationsand dNVR concentrations in a liquid containing pNVR silica particles.

DETAILED DESCRIPTION

The present invention provides a method and apparatus for determiningthe concentration of dissolved non-volatile residue (dNVR) and the sizedistribution and concentration of particulate non-volatile residue(pNVR) in a colloidal suspension.

A. Methods of the Invention.

The method involves several aspects including (a) forming droplets, forexample via aerosolization, from a sample of a colloidal suspension tobe analyzed, (b) isolating small droplets from the droplets, for exampleless than 1 um in size, (c) drying the droplets to remove the liquid,for example via evaporation, and (d) counting and sizing the residualparticles.

Importantly, the aerosol droplets isolated are small and uniformlysized, less than 1 μm and preferably a median size less than 0.5 μm. Thedroplets must be small and uniformly sized because dNVR in the dropletwill form a “residue” particle as a result of drying. If the dropletsare sufficiently small and uniformly sized, the particles formed fromthe dNVR following evaporation will be significantly smaller than theparticles initially in the liquid. In addition, small droplets are lesslikely to hold multiple particulate species that would be counted as onein the subsequent analysis.

The size of a residue particle resulting from evaporation of a liquiddroplet containing no pNVR can be determined from the concentration ofthe dNVR in the droplet using equation 1 where d_(s) is the size of thefinal residue particle, d_(d) is the size of the droplet diameter andF_(v) is the volume fraction of non-volatile residue in the droplet:d _(s) =d _(d)(F _(v))^(1/3)  (1)

If the density of the non-volatile residue in the droplet is the same asthe liquid (1.0 g/cm³ in the case of water), then F_(v) is simply theweight concentration of non-volatile residue (C). If the water has anon-volatile concentration of 1 ppm with a density of 1.0, equation 1above can be used to calculate the size of a dNVR particle resultingfrom evaporating a 0.3 μm (300 nm) droplet, as follows:d _(s) =d _(d)(C)^(1/3)=300 nm(10⁻⁶)^(1/3)=300 nm(0.01)=3 nm  (2)Hence, if the particles in the colloidal suspension are all larger than10 nm, the 3 nm particles resulting from dNVR will be <⅓ the size of thesmallest pNVR particles.

The small, uniformly sized droplets required by the present inventionmay be generated by firstly making droplets of diverse sizes andsecondly removing large droplets. Alternatively, the desired dropletsmay be made in a single step. An example of the former embodiment of themethod is implemented by generating droplets by a compressed airnebulizer or an ultrasonic nebulizer and then removing large droplets bydirecting them to an impaction surface such as a plate impactor or avirtual impactor. An example of generating small, uniform dropletsdirectly is by way of a vibrating orifice aerosol generator. After thedroplets are formed, liquid in the droplets is removed before thedroplets collide or coalesce. Liquid removal may be accomplished byheating to dry via dilution air, heated air, or heating the liquid. Itmay also be accomplished by evaporation. And after drying to isolate theparticles, the particles are counted and sized by optical particlecounters (OPC), scanning mobility particle sizers (SMPS) or otherinstruments.

Thus, referring to FIG. 1, a flow chart of a basic embodiment of themethod 10 of the invention involves the steps of, providing 11 a liquidsample, forming 12 very small, uniformly sized droplets, via an aerosol,from the liquid sample to be analyzed, drying 13, for example viaevaporating, the droplets in the aerosol, and counting and sizing 14 theresidual particles. Variants of this embodiment of the method arediscussed above.

B. Apparatus of the Invention.

Referring to FIG. 2A, one embodiment of the apparatus 20 of the presentinvention comprises means 22 for forming droplets of diverse sizesconnected to a sample input 21. Means 23 for removing large droplets iscommunicatively connected to the means 22 for forming droplets Anexample of droplet former 22 is a compressed air nebulizer, anultrasonic nebulizer, or a flow-focusing nebulizer examples of which areshown in FIG. 3A-C. An example of means 23 for isolating small uniformlysized droplets is a plate impactor or a virtual impactor (examples ofwhich are shown in FIGS. 4 and 5) having an impaction surface at whichan aerosol stream output by the nebulizer 22 is directed and whichremoves large droplets. After the desired droplets are formed, liquid inthe droplets is removed before the droplets collide or coalesce byliquid removal means 24. Examples of such means include a stream ofdilution air, heated air, or a liquid heater. Drying may also beaccomplished by a fast evaporator. A particle analyzer 25 iscommunicatively connected to the liquid remover 24. Examples of suchanalyzer for counting and sizing includes an OPC, SMPS or otherinstrument or combination of instruments. Exemplary nebulizers,impactors and analyzers are described in detail below.

Referring to FIG. 2B, another embodiment of the apparatus 30 of thepresent invention comprises means 32 for making droplets of a small anduniform size connected to a sample input 31. An example of such means isa vibrating orifice aerosol generator, an example of which is describedin detail below. After the desired droplets are formed, liquid in thedroplets is removed before the droplets collide or coalesce by liquidremoval means 33. Examples of such means include a stream of dilutionair, heated air, or a liquid heater. Drying may also be accomplished bya fast evaporator. A particle analyzer 34 is communicatively connectedto the liquid remover 33. Examples of such analyzer for counting andsizing includes an OPC, SMPS or other instrument or combination ofinstruments.

An apparatus for counting and sizing droplets formed by the dropletforming methods is shown in FIG. 2C. A test solution 51 is input to avessel 52. Solution 51 is output via a gear pump 53 through a filter 54and into a small overflow vessel 56. Most of the liquid input to vessel56 returns to vessel 52. A small portion of the liquid is sent todroplet former 55. Droplet former 55 forms an aerosol 57 containingsmall droplets. The nebulizer 55 is connected to a pressurized gassource 58, preferably compressed air or N₂. The gas is filtered, forexample via a Wafergard® filter 59. Various droplet former 55embodiments are discussed below.

The aerosol 57 is input by the droplet former 55 to a drying chamber 70.The drying chamber 70 is an elongated structure with input and outputends, a predetermined length and a predetermined horizontal dimension.The drying chamber 70 input end is connected to a source of room air viaa pump 71. Air is preferably filtered, for example via a Millipore 0.22micron Hydrophobic Millipak® filter 72. The droplet former 55 isdisposed at a predetermined location on the drying chamber 55. AScanning Mobility Particle Sizer (SMPS) 33 is disposed at apredetermined location on the drying chamber 55 a predetermined distance“L” from the nebulizer 55. A vacuum pump 74 is connected to the SMPS 33.The pump 74 operates at about 1.54 liters per minute. A thermohygrometer75, for example a DigiSense meter is disposed at the output end of thedrying chamber 70, a predetermined distance “1′” further downstream fromthe SMPS 33.

Referring to FIG. 3A, an example pneumatic nebulizer 200 which may beused to create initial droplets is disclosed. In a typical pneumaticnebulizer 200 with vent 206, compressed air exits from a small orifice201 at high velocity creating a low pressure in the exit region. The lowpressure causes liquid to be drawn into the airstream from a second tube203 from liquid reservoir 202. The high velocity air causes the liquidto accelerate and break into droplets. The high velocity spray 204 isdirected toward an impaction surface where the largest droplets areremoved and an aerosol 205 is output.

Commercially available nebulizers typically generate aerosols withdroplets whose size is log-normally distributed. Median droplet sizesare typically 0.5-5.0 μm. The geometric standard deviation is typically˜2.0. The large geometric standard deviation means that the nebulizersgenerate a significant number of large droplets. For example,approximately 0.0003% of the droplets from a nebulizer producing anaerosol with a median droplet size of 1.0 μm and geometric standarddeviation of 2.0 would be larger than 25 μm. This is in an unacceptablenumber of large droplets for the applications described above. Examplesof commercially available pneumatic nebulizers include Laskin nebulizer,Babington nebulizer, Cross-flow nebulizer, and Pre-filming nebulizer.Referring to FIGS. 3B and 3C, known concentric 210 and flow focusingpneumatic 220 nebulizers might also be used. Ultrasonic generators arealso useable for generating small droplets, but less preferred thannebulizers.

As was discussed above, large droplets can be removed from the aerosolusing either a plate impactor 300, shown in FIG. 4, or a virtualimpactor 350 as shown in FIG. 5. In the plate impactor, the platedeflects the aerosol flow to follow an abrupt 90° bend. Droplets withsufficient inertia deviate from the flow stream, impact on the plate,and are removed from the gas stream. A virtual impactor is similar to aplate impactor except that the droplets are impacted into a quiescentregion where they are withdrawn from the aerosol by a small secondaryflow.

The effectiveness of impactors for removing particles is related to theStokes number or impaction parameter. The Stokes number (S_(tk)) isproportional to the square of the droplet size as shown in equation 3where ρ_(p) is the droplet density, U is the nozzle velocity, η is thegas viscosity, and D_(j) is the nozzle diameter.S _(tk)=(ρ_(p) d _(p) ² U)/(9ηD _(j))  (3)

Impactors can be designed with sharp efficiency curves. An impactordesigned to remove 50% of the droplets >10 μm should remove virtuallyall droplets >25 μm. An example of a typical impactor efficiency curveis shown in FIG. 6.

Another approach to generating an aerosol with small droplets is throughthe use of a vibrating orifice aerosol generator 400. Referring to FIG.7, these generators 400 work by vibrating a liquid at a high frequencyas it passes through a small orifice. They produce nearly monodispersedroplets. The size of the droplets generated can be calculated usingequation 4 where Q_(L) is the liquid flow rate and f is the oscillatingfrequency:d _(d)=(6Q _(L) /πf)^(1/3)  (4)A generator operating at 2 MHz with a flow rate of 0.02 ml/min wouldproduce 10 μm droplets.

A preferred approach involves a system including a combinationnebulizer-impactor 450. Referring to FIGS. 8-10, an input conduit 428transfers fluid to a pneumatic nebulizer portion of the system. Thenebulizer 450 also receives air, nitrogen or another gas under pressurefrom a pressurized gas source through conduit 460. Within nebulizer 450,the liquid sample and compressed gas are merged to generate an aerosolincluding droplets of the liquid sample suspended in the gas.

Nebulizer 450 includes a reservoir 468 in fluid communication with themerger zone. The reservoir 468 collects most of the liquid suppliedthrough the input conduit 428, i.e. the liquid not used to form theaerosol droplets.

The inclined orientation shown is advantageous for liquid drainage andevacuation, although not critical. A housing of the nebulizer 450 hasseveral integrally coupled sections, including a stainless steel housingsection 472 that encloses merger zone 448, a steel housing section 474forming the aerosol conditioning zone, and a housing section 476providing the reservoir 468. Housing section 472 supports a fitting 478for receiving the air or other compressed gas from conduit 460. Thishousing section 472 also supports an impactor 480, through a threadedengagement that permits adjustment of the axial spacing between impactor480 and merger zone 448.

With reference to FIG. 9, housing section 472 further supports athermoelectric device 482 that functions to maintain a stabletemperature of about 30.degree. C. in the vicinity of merger zone 448.More particularly, the thermoelectric device 482 extracts heat fromhousing section 472 and transfers it to a heat sink 484. Thethermoelectric device 482 also may function as a heater for thenebulizer. The constant temperature promotes consistent dropletformation. Housing section 472 further supports bulkhead fitting 446,which secures an input conduit 428 used to transfer the sample liquid tomerger zone 448.

As best seen in FIG. 10, merger zone 448 takes the form of a cylindricalchamber in a Teflon orifice housing 473. A sapphire orifice plate 486defines an entrance or primary orifice to receive pressurized gas intothe chamber from conduit 460. A sapphire orifice plate 488 defines anexit or secondary orifice through which the merged liquid and gas leavethe chamber. In addition, a liquid receiving entrance 490 conducts thesample liquid into the chamber.

In one suitable version of nebulizer 450, primary orifice 486 has adiameter of 0.006 inches, and secondary orifice 488 has a diameter of0.008 inches. The chamber 448 has a diameter of 0.020 inches, and anaxial length, i.e. space in between orifice plates 486 and 488, of 0.020inches.

More generally, the secondary orifice 488 diameter is larger than theprimary orifice 486 diameter, yet less than the diameter of thecylindrical chamber 448. As compared to prior devices in which there isno secondary orifice 488 and the chamber is simply open at the exit end,there is a back pressure due to the secondary orifice which increasesthe feed pressure to the merger zone 448 and results in a higher kineticenergy mixing of the liquid and compressed gas. This advantageouslyresults in smaller sample liquid droplets in the aerosol leaving themerger zone 448.

As the size of the secondary orifice 488 is reduced, the droplet size isreduced and the back pressure is increased. When the sample liquid iswater, it has been found satisfactory to form the secondary orifice 488and the primary orifice 486 at a diameter ratio of 2 to 1 as indicatedby the diameters given above. For a sample liquid with a boiling pointlower than water, the preferred diameter ratio is closer to 1, yet thesecondary orifice 488 remains larger than the primary orifice 486.

The higher energy in the merger zone 448 more effectively breaks up theliquid. The secondary orifice 488 also appears to improve the efficiencyof the impactor 480 downstream. The ratios of primary 486 and secondary488 orifice diameters can be selected to vary the pressure at the liquidentrance to the merger zone, relative to atmospheric pressure. Dependingon the diameter ratio, air inlet pressure and liquid flow rate theliquid pressure can be adjusted from below atmospheric pressure to apressure nearly equal to the inlet air pressure.

As seen in FIG. 10, impactor 480 is disposed coaxially with merger zone448, spaced apart in the axial direction from orifice plate 488. Theimpactor 480 cooperates with housing section 472 to form a thin,somewhat hemispherical path to accommodate the flow of air and dropletsbeyond the merger zone 448. The smaller droplets tend to follow the airflow, while the larger droplets tend to collide with impactor 480 andare removed from the aerosol stream. Thus, the aerosol moving intoconditioning zone 462, upwardly and to the right as viewed in FIG. 8,includes only those droplets below a size threshold determined largelyby the axial spacing between secondary orifice 488 and impactor 480. Thesize threshold is increased by increasing the axial spacing, and reducedby moving the impactor 480 closer to orifice plate 488.

The droplets impinging upon impactor 480 may remain on the impactor 480momentarily, but eventually descend to reservoir 468 then drain from thenebulizer 450. If desired, impactor 480 may be formed of sintered metalto provide a porous structure that more effectively prevents the larger,impacting droplets from interfering with the aerosol flow.

A secondary gas may be introduced into nebulizer 450 at a locationupstream of the nebulization region. The secondary gas sweeps dead spacein the nebulization region resulting in a faster response, reduced axialdiffusion, and less smearing of the output due to mixing.

As was discussed above in general, once the aerosol is formed, theliquid in the droplets must be evaporated before the droplets have achance to collide and coalesce. Drying can be accomplished usingdilution air, heated air or heating the liquid.

Once the liquid is evaporated, the particles in the aerosol can becounted and sized by a number of techniques including, but not limitedto Optical Particle Counters (OPCs), and Scanning Mobility ParticleSizers (SMPS). OPCs are similar to those used in liquids. They size andcount individual particles as they pass through a laser beam. Examplesof OPCs include those made by Particle Measuring Systems, RION, Horiba,Particle Sizing Systems, and Hach Ultra.

In summary, the preferred embodiment of the apparatus of the inventionincludes the Nebulizer/Impactor 450 and a Scanning Mobility ParticleSizer (SMPS). This embodiment is believed to be best suited formeasurement of dNVR concentration and pNVR PSD.

Although the apparatus and method of the invention has been described inconnection with the field of semiconductor device manufacture, it canreadily be appreciated that it is not limited solely to such field, andcan be used in other fields.

FIG. 11 is a graph of droplet size distributions (differentialconcentration vs. droplet diameter measured in um) produced by variouscombinations of nebulizers with or without impactors A-D. Differentialconcentration is measured in d (#/cm³) per d log(D_(p)). The graphincludes lines illustrating fits of the PSD to a log-normaldistribution. The droplet size distributions were measured by forming anaerosol from a sucrose solution, drying the droplets, measuring theresidue PSD and calculating the droplet PSD using the equations above.The graph shows that Combination D has the best distribution in that ithas the smallest and most uniform droplets, and virtually no dropletsare larger than 10 um.

FIG. 12 is a graph of differential residual concentration (d(nm³/cm³)/dlog(D_(p))) versus particle size (in nm) which shows the ability to size30 nm polystyrene latex (PSL) particles. One sizing was conducted with aCombination D apparatus (FIG. 11) with an SMPS detector. Another wasconducted with a dynamic light scattering (DLS) instrument, moreparticularly with a NICOMP 380ZLS made by Particle Sizing Systems, SantaBarbara, Calif. The comparison shows generally good agreement. TheCombination D apparatus with SMPS analyzer permits measurement of actualnumber concentration. In contrast, DLS only provides relativeconcentrations. Number concentrations can be measured directly byassemblies like Combination D with SMPS analyzer by calibrating theinstrument liquid sampling flow rate using a colloidal suspension with aknown volume concentration of pNVR and very little dNVR. Calibration isperformed by inputting the suspension into Combination D with SMPSanalyzer under controlled conditions and measuring the resultingvolume-weighted PSD and calculating the liquid sampling rate usingequation 5:F ₁=(C _(pa) /C _(pl))F _(a)  (5)Where F₁ is the instrument liquid sampling flow rate, C_(pa) is thevolume concentration of particles in the aerosol, C_(pl) is the volumeconcentration of particles in the suspension, and F_(a) is the aerosolflow rate. FIG. 13 shows the mass distribution measured following inputof 5.0×10¹⁷ nm³/mL suspensions of silica particles into combination Dwith SMPS analyzer. In this case the liquid sampling flow rate was foundto be 0.205 μL/min.The Combination D apparatus with SMPS analyzer also provides a moredetailed measurement of PSD than DLS that most often assumes that theparticles in the colloidal suspension are log-normally distributed. FIG.14A is a graph of differential volume concentration vs. particlediameter for a colloidal dispersion measured using a Combination Dapparatus with an SMPS detector. FIG. 14B shows the PSD measured usingDLS and FIG. 14C shows images of the particles in the slurry fromscanning electron microscopy (SEM). The Combination D apparatus withSMPS analyzer and the SEM analyses both indicate that the particles havea trimodal distribution; an aspect of the distribution that was notdetected by the DLS analysis.

Measurement of actual number concentration measurement also allowsdetermination of changes in PSD that are undetectable using instrumentsthat only measure relative concentrations. FIGS. 15A and 15B showchanges in slurry number-weighted and volume-weighted PSD over timeduring handling via graphs of differential concentration versus particlediameter. Successive times 1-9 are graphed. The number and volume ofsmaller particles decrease over time while the number and mass of largerparticles (i.e. greater than approximately 250 nm) increases. Thisindicates that particle agglomeration is occurring due to handling.These changes were not detected by DLS (FIG. 15C).

FIG. 16A is a graph of the PSD from a colloidal dispersion of silicaparticles containing a high concentration of dNVR measured usingCombination D with SMPS analyzer. In this case the dispersion contained0.1% by weight pNVR and 1% by weight dNVR. The peak occurring ˜29 nm isdue to the pNVR while the high concentration of smaller particlesresults from the dNVR. There is poor separation between the pNVR anddNVR signals. However, by diluting the dispersion prior to input intothe Combination D/SMPS analyzer separation can easily be achieved asshown in FIG. 16B. The separation does not occur if the smaller particlesignal is due to a bimodal distribution of pNVR particles as shown inFIG. 17.

FIG. 18A is a graph showing measurements of a colloidal suspension ofsilica particles containing different concentrations of dNVR. Theconcentration of small particles is seen to increase with increasingdNVR concentration. The increase is monotonic with concentration asshown in FIG. 18B.

The embodiments above are chosen, described and illustrated so thatpersons skilled in the art will be able to understand the invention andthe manner and process of making and using it. The descriptions and theaccompanying drawings should be interpreted in the illustrative and notthe exhaustive or limited sense. The invention is not intended to belimited to the exact forms disclosed. While the application attempts todisclose all of the embodiments of the invention that are reasonablyforeseeable, there may be unforeseeable insubstantial modifications thatremain as equivalents. It should be understood by persons skilled in theart that there may be other embodiments than those disclosed which fallwithin the scope of the invention as defined by the claims. Where aclaim, if any, is expressed as a means or step for performing aspecified function it is intended that such claim be construed to coverthe corresponding structure material, or acts described in thespecification and equivalents thereof, including both structuralequivalents and equivalent structures, material-based equivalents andequivalent materials, and act-based equivalents and equivalent acts.

What is claimed is:
 1. An analysis apparatus, comprising a dropletformer for forming small droplets less than 10 um in diameter, anevaporator communicatively connected to the droplet former, and adetector communicatively connected to the evaporator for detectingdissolved and particulate residues, wherein the droplet former iscalibrated using a liquid volumetric inspection rate which is determinedby inputting a colloidal suspension with a known volumetricconcentration of particulate residue, and measuring the volumetricconcentration of particulate residue by: a. forming an aerosolcontaining droplets from the liquid; b. isolating the small less than 10um diameter, uniformly sized droplets from the droplets; c. removingliquid from the small less than 10 um diameter, uniformly sized dropletsto form dissolved residue particles and particulate residue particles,and d. analyzing dissolved and particulate residue particles by countingand sizing.
 2. An analysis apparatus for measuring dissolved residueconcentration and particulate residue concentration and particle sizedistribution in colloidal suspensions and wherein the liquid andparticles are in a colloidal suspension, comprising: a. anebulizer/impactor for forming droplets and for isolating small lessthan 10 um in diameter, uniformly sized droplets therefrom, thenebulizer/impactor comprising a housing forming a mixing chamberincluding: (i) a liquid entrance for receiving a sample colloidalsuspension into the chamber; (ii) a primary orifice having a firstdiameter for receiving a pressurized gas into the chamber for mergerwith the sample suspension to generate an aerosol composed of multipledroplets of the sample liquid suspended in the gas; (iii) a secondaryorifice having a second diameter for conducting the aerosol out of thechamber; and (iv) an impactor coaxial with the mixing chamber and spacedapart axially from the secondary orifice downstream of the chamber, saidimpactor having a convex upstream surface cooperating with a concavesurface of the housing to form a generally hemispherical path forconveying the aerosol away from the chamber; b. an evaporatorcommunicatively connected to the nebulizer/impactor for removing liquidfrom the droplets and generating dissolved residue and particulateparticles; and c. an analyzer, communicatively connected to theevaporator, for counting and sizing dissolved and particulate residueparticles; and wherein a liquid volumetric inspection rate forcalibrating the apparatus is determined by inputting a colloidalsuspension with a known volumetric concentration of particulate residueand measuring the volumetric concentration of particulate residue in theaerosol produced by: i. forming an aerosol containing droplets from theliquid; ii. isolating small less than 10 um diameter, uniformly sizeddroplets from the droplets; iii. removing liquid from the small lessthan 10 um diameter, uniformly sized droplets to form dissolved residueparticles and particulate residue particles; and iv. analyzing dissolvedand particulate residue particles by counting and sizing.